Resources to assess frost damage for corn and soybeans

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Below-freezing temperatures Sunday and Monday morning, May 9 and 10, across the southern half of the Lower Peninsula have exposed early planted corn and soybeans to potentially lethal conditions. Numerous 29°F and 30°F temperatures were observed across the region early Sunday morning by Enviro-weather, with a low of 28.7°F occurring at Lakeview in Montcalm county. Monday morning temperatures dipped lower, ranging from 28°F to 30°F across the southern half of the state. Bath, in Clinton County, recorded 27.5°F; Belding, in Ionia county, saw 27.0°F; and Leslie, in Ingham County, was the regional low at 24.8°F.

Initial frost damage to corn can look pretty lethal, but as long as the growing point remains viable, corn plants should be able to make a full recovery. The growing point for a corn plant won’t emerge from below the soil surface until the V5 or V6 growth stage. A hard frost may kill above ground tissue, but as long as the growing point is alive, the plant should be able to push the dead material up and out from the whorl. Good growing conditions for several days following a frost event will yield evidence of new growth, but this week’s cool and possibly wet forecast may hinder determination of corn survival from frost.

Soybean plants can actually endure colder temperatures and a longer duration of those temperatures than corn. The lethality of freezing temperatures to soybeans can be more severe, however, with the above ground location of soybean growing points. When assessing soybean frost damage, it’s important to remember that in addition to the terminal growing point located at the top of the main stem, soybeans can also produce new growth from vegetative growing points located in the leaf axils on the main stem if the terminal growing point is lost. Like corn, the true extent of frost damage isn’t likely to be apparent for several days following the freeze event and the soybean plant is given a chance to demonstrate regrowth.

Late last week’s rain likely helped us limit the damage potential. Crops can be injured by below ground freezing temperatures just as they can by above ground freezing temperatures. Certain soil conditions such as loose, recently tilled soil, coarse texture, and low soil moisture can all aid in freezing temperatures permeating below ground. Soil moisture levels right now are fairly high, insulating soil to some extent against the low nightly air temperatures.

A number of useful resources exist for diagnosing frost damage to corn and soybean and the factors than need to go into determining if replanting is necessary. Purdue’s Bob Nielsen shows frost injury to corn and soybeans on his website (http://www.agry.purdue.edu/ext/corn/news/articles.01/Frost_Corn_Soy-0418_Gallery.html), while illustrating the keys to examine for regrowth potential.

Hard frosts can do a fairly complete job of eliminating a corn or soybean stand, but moderate freezes like we’ve seen the last several nights can result in spotty crop death. In cases like these, replanting decisions become more difficult. Purdue’s “Estimating Yield and Dollar Returns From Corn Replanting” (http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf) and Iowa State’s “Soybean Replant Decisions” (http://www.extension.iastate.edu/publications/pm1851.pdf) are both excellent resources for aiding in the decision to replant reduced stands.

Hopefully, the freezing events over the last several nights will be our last frost for the spring. Remember that the true extent of any injury may not be evident for several days. The rain from late last week and that forecast for Tuesday, May 11, may prevent us from doing quick replants anyway. Luckily, we’ve got lots of season left to go.

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